Brenda Ann wrote in message
...

"N_Cook" wrote in message
...
No user switchable option. I can see its possible to rewire the vibrator
so
you still get right polarity for the anode supplies. Heaters presumably
happy enough powered the other way round but how to change the biasing
of
the valves ?



Unless it's a synchronous vibrator, it should run equally well on either
polarity. The radio doesn't get anode voltage from the car's DC, it gets
it
from the radio's DC-DC converter (vibrator, transformer, rectifier,
filtering).




With positive ground you automaticly get a negative voltage for biasing but
what to do in the negative ground case ?
In this case its a synchronous mechanism but its easy enough to get inside
to rewire it for the opposite polarity, it is the biasing voltage I cannot
fathom out.